A fundamental challenge facing neuro-oncologists is how to ameliorate the morbidity and mortality occurring as a side effect of radiation. Brain radionecrosis, the most significant complication associated with radiation therapy for treating brain tumors, is a spectrum of disease from edema to tissue necrosis. In those it does not kill, it can be devastating with significant morbidity associated. There is no known treatment that can mitigate the injury for all patients. An alternative therapy is a fundamental necessity. We propose to demonstrate the utility and effectiveness of a complementary therapy: Hyperbaric Oxygen Therapy (HBOT). This alternative therapy may be a powerful means to ameliorate the devastating consequences of radionecrosis of the brain. HBOT is successfully used as an adjunctive treatment for radionecrosis in bone and soft tissue. By promoting angiogenesis, revascularization of the injured tissue is facilitated. We believe similar revascularization might occur in neural tissue but this is not proven. The main objectives of this project are to 1) obtain pilot data demonstrating the potential for increased benefit when complementing conventional steroid therapy with HBOT for brain radionecrosis patients, 2) estimate the magnitude of benefit of HBOT to brain radionecrosis patients using objective measures of neurologic function, radiographic imaging and standardized quality of life measures, and 3) obtain preliminary data of the effect of HBOT on cerebral revascularization using perfusion MRI. Our central hypothesis is that conventional care with complementary HBOT will result in decreased neurologic deficit, increased quality of life, and decreased progression or reversal of brain radionecrosis when compared to conventional care alone. We will randomize consenting patients to either steroid therapy or steroid therapy with HBOT. We will use standardized physical examinations, PET scans, MRI and health related quality of life questionnaires to evaluate outcomes. Outcomes will be measured at regular intervals during and after treatment. Perfusion MRI will be used to investigate the process of revascularization. We will use these results to appropriately design future studies to more fully evaluate the use of HBOT in brain radionecrosis. Demonstrating a reduction in neural injury and its sequelae by using HBOT has the potential to fill the void of successful treatments available to brain radionecrosis patients.